1. Field of the Invention
This invention generally relates to a rotary driving mechanism for driving to rotate a rotating shaft intermittently over a predetermined angle and in particular to a rotary solenoid including a rotatable rotor, stator with magnetic poles and a coil whereby the stator is periodically energized by the coil to cause the rotor to rotate back and forth over a predetermined angle. More specifically, the present invention relates to an ink ribbon feeding apparatus of a printer for driving to move the ink ribbon housed in an ink ribbon cartridge intermittently at high speed as characters are printed on paper.
2. Description of the Prior Art
In typewriters and printers, an ink ribbon cartridge is widely used because of its convenience. The ink ribbon cartridge is usually comprised of a housing, a supply reel, a take-up reel and an ink ribbon which is wound around the supply reel before use. It is necessary to provide a driving mechanism in a printer to drive to move the ink ribbon intermittently at a predetermined pitch when desired characters are to be imprinted on paper with the ink ribbon cartridge mounted in position. In particular, in a serial printer, the ink ribbon must be moved over a predetermined distance after printing a selected character at high speed.
A rotary solenoid has been used in a printer to drive to move the ink ribbon intermittently. Such a rotary solenoid typically includes a rotor fixedly mounted on a rotatable shaft, a stator provided with magnetic poles, a driving coil which is periodically energized to cause magnetic interaction between the rotor and the stator and a one-way clutch for converting the oscillating rotary motion into incremental intermittent rotary motion. The driving shaft provided at the output side of the one-way clutch is operatively coupled to the take-up reel when the ink ribbon cartridge is mounted in position, so that the ink ribbon may be advanced incrementally by operating the rotary solenoid. However, as printing speed increases, driving power requirements are increased. Thus there has been a need for developing a high power rotary solenoid which may be advantageously applied in high speed typewriters and printers. It is also necessary to keep the rotary solenoid compact in size even if its capacity is increased because it will prevent the typewriter or printer from becoming bulky.